COMPOSITE MATERIAL WITH GRADUALLY DISSOLVING COATING FILM AND COATING COMPOSITION

摘要

A composite material comprising a base having a hard surface and a gradually dissolving coating film formed at ordinary temperature on that part of the surface which occasionally comes into contact with water, characterized in that the gradually dissolving coating film comprises at least one water-soluble polymer selected from the group consisting of polyvinyl alcohol, polyacrylamide, and hydroxyethyl cellulose and a metal salt forming a hydroxide sparingly soluble in water. Since the gradually dissolving coating film has metal hydroxide clusters therein, the rate of water infiltration in the film-thickness direction is reduced. When water flows away, only that part of the coating film which is located near to the film surface and into which water has infiltrated is washed away. Consequently, the coating film does not wholly disappear at a time.